<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
</head>

<body>
  <script>
    // 
    function fn(a, b) {
      console.log(this.x + this.y + a + b);
    }

    const o = {
      x: 10,
      y: 20,
    };

    fn.call(o, 30, 40)

    // fn(30, 40);

    // fn();
  </script>
</body>

</html>